1. Field of the Invention
The present invention relates to a flow control valve for controlling flow between a fuel tank in an automobile or the like, and the outside.
2. Description of the Related Art
One known related art design for a flow control valve includes a circulation unit for circulating fuel vapors inside the fuel tank, disposed between the inlet pipe and the canister (JP-A 8-216707). The circulation unit includes a breather pipe that connects the filler neck with the fuel tank interior; and a flow control valve disposed at the inlet of the breather pipe. The flow control valve is situated inside the breather pipe passage and features a check valve having a ball valve and a spring, and is designed to open and shut in response to pressure applied to the ball valve. According to this feature, utilizing the rise in tank internal pressure of the fuel tank that occurs during fueling, the flow control valve is opened only when a prescribed pressure is exceeded, whereby fuel vapors inside the fuel tank are circulated to the filler neck through the breather pipe, thereby reducing the amount of outside air drawn in from outside the filler neck and reducing the amount of fuel vapors produced.
However, according to the flow control valve, if the pressure-receiving surface area of the ball valve is larger in size for increasing the ventilation volume of fuel vapors and achieving smooth circulation of the fuel vapors, the breather pipe and the passage diameter thereof must unavoidably be larger as well, creating the problem of larger scale. Moreover, during fueling, the fuel gun has the characteristic of a low flow rate in the initial period following pushing of the fueling switch, followed by rapid increase thereafter. In order to compensate for this characteristic, it would be preferable for the flow control valve to have a small aperture at low pressure, and for the aperture to increase rapidly as the pressure rises. However, a problem with conventional flow control valves is that valve opening characteristics like those described above are difficult to achieve.